When a ray of light is incident on a glass slab at an angle of 60 ∘ the angle between the reflected and refracted rays is 90 ∘ the refractive index of glass is?

Sometimes while applying the Snell's law of refraction, you will receive the sin(Θ₂) as a value greater than 1. This is, of course, impossible - our Snell's law calculator will display the value as "NaN". If this happens, it means that all light is reflected from the boundary (this phenomenon is known as the total internal reflection).

The highest angle of incidence, for which the light is not reflected, is called the critical angle. The refracted ray travels along the boundary between both media. It means that the angle of refraction is equal to 90°. Hence, you can find the critical angle by using the following equation:

n₁sin(θ₁) = n₂sin(90°)

After simplification, n₁sin(θ₁) = n₂ * 1.

Solving for the angle of incidence, Θ₁ = arcsin(n₂/n₁).

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